In the field of communication cables, there have been recent advances whch make use of fiber optic conductors to provide wide band transmission channels. These cables, because of the delicate nature of the fiberglass conductors, were previously assembled by wrapping the glass strand over a strength member core and placing fillers or spacers around and between the glass conductors in an attempt to protect them from damage.
Strength member cores with extruded grooves or splines have been tried with only fair success, because of the variability of the pitch of the helix resulting from the difficulty of accurately forming such grooves in extruded plastic materials, and in particular foamed plastic materials.
This invention provides apparatus and method for forming precise helical grooves in the plastic layer of insulation which covers a strength member, and simultaneously placing the fiber optic and electrical conductors into their assigned grooves in the making of the fiber optic cable.
In apparatus for assembling a communication cable containing both fiber optic and electrical conductors, there is a payoff unit for the covered strength member, a rotating driven cutter support plate on which are mounted one or more self-driven cutter heads which are powered by electricity furnished through slip rings, a guide tube for the core into and out of the cutter head, payoff members for the fiber optic and electrical conductors which are carried on supply reels mounted on the driven rotating guide tube. The apparatus also includes driven binder heads, a driven capstan to pull the cable as it is being formed through the various operations, payoff members to hold the insulating tapes that are folded over the core with the necessary forming and guide mechanisms, the driven rotating binder heads to hold the insulating tapes in place and a driven take-up unit. All units of this apparatus are carefully synchronized by electrical and mechanical means so that the grooves are cut to an exact, predetermined pitch and depth, and the conductors are placed precisely into their assigned grooves.
Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.